The structure and properties of medium-chain surfactant solutions: a case study of sodium octanoate

Rosenholm, Jarl B.

doi:10.1016/0001-8686(92)80013-n

Cited by 17 publications

(7 citation statements)

References 107 publications

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“…For instance, the system closer to interface saturation (N = 50) reached an average concentration of octanoate at the midplane of the simulation box of ca. 0.03 mol L −1 (about 10-fold lower than the cmc), 19 in contrast to the much larger concentration at the interfaces of ca. 4 mol L −1 (about 10-fold higher than the cmc).…”

Section: ■ Introductionmentioning

confidence: 77%

“…There were two reasons to choose sodium octanoate: first, short-chained surfactants present fast structural and energetic relaxation in bulk simulations, − allowing a proper sampling of the equilibrium states to be achieved within affordable computer times, and second, sodium octanoate has a large cmc value, rendering realistic model systems much smaller than those describing surfactants with longer hydrophobic tails.…”

Section: Methodsmentioning

confidence: 99%

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Surface Electrostatic Potential and Water Orientation in the presence of Sodium Octanoate Dilute Monolayers Studied by Means of Molecular Dynamics Simulations

Bernardino

Moura

2015

Langmuir

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A series of atomistic molecular dynamics simulations were performed in the present investigation to assess the spontaneous formation of surfactant monolayers of sodium octanoate at the water-vacuum interface. The surfactant surface coverage increased until a saturation threshold was achieved, after which any further surfactant addition led to the formation of micellar aggregates within the solution. The saturated films were not densely packed, as might be expected for short-chained surfactants, and all films regardless of the surface coverage presented surfactant molecules with the same ordering pattern, namely, with the ionic heads toward the aqueous solution and the tails lying nearly parallel to the interface. The major contributions to the electrostatic surface potential came from the charged heads and the counterion distribution, which nearly canceled out each other. The balance between the oppositely charged ions rendered the electrostatic contributions from water meaningful, amounting to ca. 10% of the contributions arising from the ionic species. And even the aliphatic tails, whose atoms bear relatively small partial atomic charges as compared to the polar molecules and molecular fragments, contributed with ca. 20% of the total electrostatic surface potential of the systems under investigation. Although the aliphatic tails were not so orderly arranged as in a compact film, the C-H bonds assumed a preferential orientation, leading to an increased contribution to the electrostatic properties of the interface. The most prominent feature arising from the partitioning of the electrostatic potential into individual contributions was the long-range ordering of the water molecules. This ordering of the water molecules produced a repulsive dipole-dipole interaction between the two interfaces, which increased with the surface coverage. Only for a water layer wider than 10 nm was true bulk behavior observed, and the repulsive dipole-dipole interaction faded away.

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Section: ■ Introductionmentioning

confidence: 77%

Section: Methodsmentioning

confidence: 99%

Surface Electrostatic Potential and Water Orientation in the presence of Sodium Octanoate Dilute Monolayers Studied by Means of Molecular Dynamics Simulations

Bernardino

Moura

2015

Langmuir

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“…We have previously demonstrated that the first methylene group attached to the carboxylate moiety behaves as a polar group, even though its atoms are typically apolar in the force-field description . This behavior had already been reported in experimental investigations and is usually described as an electrorestriction effect . Bearing in mind this unique characteristic of the first methylene group, the octanoate molecule should be split into a hexane-like tail and an acetate-like head.…”

Section: Methodsmentioning

confidence: 84%

“…The sodium octanoate concentration was ca. 0.7 M, which is about twice the critical micelle concentration (cmc) value for this surfactant and well bellow the second critical concentration . The proper choice for the surfactant concentration is mandatory for simulations of micellar systems in order to ensure that aggregates remain stable and belong in the correct phase.…”

Section: Methodsmentioning

confidence: 97%

Aggregation Thermodynamics of Sodium Octanoate Micelles Studied by Means of Molecular Dynamics Simulations

Bernardino

Moura

2013

J. Phys. Chem. B

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The present work is aimed at studying the computation of the thermodynamic potentials that describe the stability of anionic surfactant molecules in micellar aggregates. We report a set of molecular dynamics simulations of a sodium octanoate micelle in aqueous solution using the umbrella sampling method along with the Jarzynski equality in order to compute the potential of mean force for the dissociation process of one surfactant molecule from a previously assembled micellar aggregate. The Jarzynski average was computed at several different temperatures in order to estimate the Gibbs energy of association for the octanoate anion, which was split into its enthalpic and entropic contributions. We also estimated the contributions arising from the polar head and the apolar tail for each thermodynamic potential, and a detailed picture emerged from these simulations. The aggregation is driven mostly by the Gibbs energy contribution arising from the hydrophobic tail, which was large enough to cancel out the unfavorable contribution from the polar head. Although the association process may be ascribed mostly to the transfer of the apolar tail to the micellar core, it should be noted that the polar head also contributed with a favorable entropic term to the overall Gibbs energy. These findings were rationalized by comparing the energetic and structural patterns of the hydration process of a free monomer in solution to an aggregated molecule. The interaction energy distributions presented at least two discernible populations and each population was related to a different structural pattern, as characterized by the radial distribution functions. Altogether, the changes in both the energy and structure of the hydration layer are consistent with the entropy-driven association of the surfactant into the micellar aggregate.

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“…Eur class (AppliChem) was used. The critical micelle concentration (CMC) of NaC8 at which spherical micelles are formed is around 330 -370 mM [8]. From the initial suspensions, two aqueous suspensions with concentration 0.5 g/L for DND-COOH and 0.25 g/L for DND-H were prepared.…”

Section: Experimental Partmentioning

confidence: 99%

Interactions of nanodiamonds and surfactants in aqueous suspensions

Vervald¹,

Burikov²,

Vlasov³

et al. 2018

Nanosystems: Phys. Chem. Math.

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In this study, with the use of laser Raman spectroscopy the significant difference in intermolecular interactions of detonation nanodiamonds with hydrophilic and hydrophobic surface groups in aqueous solution of surfactants was observed. It was found that at low concentrations of sodium octanoate (before the micelle formation) the weakening of hydrogen bonds by nanodiamonds has a different dynamics for hydrophobic and hydrophilic nanodiamonds. However, with the addition of surfactants, this effect gradually decreases for both types of nanodiamonds and ends after the formation of micelles. Such effects are explained by the "shielding" effect of surfactant molecules surrounding nanodiamond particles.

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The structure and properties of medium-chain surfactant solutions: a case study of sodium octanoate

Cited by 17 publications

References 107 publications

Surface Electrostatic Potential and Water Orientation in the presence of Sodium Octanoate Dilute Monolayers Studied by Means of Molecular Dynamics Simulations

Surface Electrostatic Potential and Water Orientation in the presence of Sodium Octanoate Dilute Monolayers Studied by Means of Molecular Dynamics Simulations

Aggregation Thermodynamics of Sodium Octanoate Micelles Studied by Means of Molecular Dynamics Simulations

Interactions of nanodiamonds and surfactants in aqueous suspensions

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